Kim Jong-un's regime said late on Tuesday that it may strike Guam. That came shortly after Trump warned Pyongyang it would face "power, the likes of which this world has never seen before" if the renegade state continued to threaten the U.S.
"If the red line he drew today was 'North Korea cannot threaten the U.S. anymore,' that line was crossed within an hour of him making that statement," said John Delury, associate professor of Chinese studies at Seoul-based Yonsei University.
The episode draws parallels to President Barack Obama's own geopolitical red line.
In 2013, the former leader said the use of chemical weapons in Syria's civil war would trigger an American military response. But when it happened, Obama failed to follow up on his promise — a move that critics, including Trump, said weakened Washington's position as a superpower.
"Trump is drawing a decisive red line for himself, we all think back to Obama's red line in Syria, which ultimately became an embarrassment for him," Peter Jennings, Australia's former deputy secretary in defense, told CNBC.